Many manufacturing processes are monitored using sensors that detect a physical phenomena such as movement or position of an actuator at a sensing site. In one form a detection sensor is connected to two-wires for carrying either alternating current or direct current signals between the sensor and a monitoring circuit that determines a status (open or closed) of a switch within the sensor.
Other sensors require a three-wire input to the sensor. One of the three-wires provides a sensor power input for energizing circuitry at the sensor site. The so-called three-wire sensors are divided into two categories. If the sensor circuitry sinks current, it draws current into the sensor from the monitoring circuit to a ground potential coupled to the sensor by a ground connection. If the sensor circuitry is a source of current, energy supplied by the power input to the sensor is output in the form of a current signal from the sensor to the monitoring circuit.
The choice between a two-wire and a three-wire sensor is based at least in part upon cost, current or power consumption and response time. Generally, suitable two-wire and three-wire sensors can be used in most applications.
Namco Controls Corporation, assignee of the present invention, markets monitoring systems for determining the status of sensing circuits. Heretofore, special interfacing was required depending upon the type of sensor the circuit was monitoring. The present invention concerns a universal input or interface for mating with a sensor that automatically provides signals corresponding to the state of the sensor regardless of the type of sensor.